Why too much mulch can be harmful to your trees
I have a tree in my yard, planted before I purchased this house, that’s covered up by about 16 inches of mulch. Will it kill the tree if I remove the dirt to ground level?
—Dan Draia, Charlotte, NC
Your tree may have already been fatally harmed due to this unfortunate buildup of mulch and soil, so it’s hard to say for sure that your tree will survive after you remove them. But you can be sure that if you don’t remove them, then there’s no question that the tree will die.
Mulch around the base of a tree can serve a useful purpose as a weed suppressant, an insulator against the sun’s heat, a moisture reservoir, and a boundary to keep away bark-damaging string trimmers. But that mulch should be no more than 2 inches thick and not touch the bark at all.
Piling a “mulch volcano,” or in your case a “mulch-and-soil volcano” on top of the roots deprives them of the oxygen they need to grow, and encourages them send secondary roots up into the mulch. These roots are more vulnerable to drying out and freezing, and can form girdling roots that encircle the trunk and cut off the flow of nutrients between leaves and roots.
To get rid of your volcano, remove the stones, then take a hand cultivator and gently comb away the mulch and soil down to the original grade. Try not to cut or scar the main root system radiating out from the trunk just below grade. But when you encounter small upward-growing roots, snip them off at their base with pruning shears. And if you find circling roots that might strangle the trunk, cut them back as well.
Stop excavating once you’ve exposed the trunk’s root flare, when the trunk naturally slopes into the ground. Water the freshly exposed ground, then add a layer of fresh mulch as described above. With any luck, your work will rejuvenate the root system and enable the tree to survive and flourish.
See what TOH landscape contractor Roger Cook does to get rid of mulch volcanoes.
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